1. Field of the Invention
The invention generally relates to a projection apparatus, and more particularly, to a projection apparatus with improved light use efficiency.
2. Description of Related Art
Generally speaking, a conventional projection apparatus includes two lens arrays and a digital micro-mirror device (DMD). Each of the lens arrays includes a plurality of lens cells, and the lens cells in the two lens arrays are respectively corresponding to each other. A light beam can be led to the DMD by the lens cells in the lens arrays so that a light spot is shaped and uniformed. However, because the DMD in a conventional projection apparatus has a rectangular contour, the lens cells should also be a rectangle in order to produce a well-shaped and uniform light spot on the DMD.
In a conventional projection apparatus, the lens array closer to the light source has a specific valid range of the light collection angle. When a light beam from the light source radiates toward a lens cell in the lens array closer to the light source at an angle within the valid range of the light collection angle, the light beam is led to the corresponding lens cell in the other lens array and then to the DMD. However, when the light beam reaches a lens cell in the lens array closer to the light source at an angle outside the valid range of the light collection angle, the light beam is not led to the corresponding lens cell but a lens cell beside the corresponding lens in the other lens array. Thus, the travel direction of the light beam appears to deviate from the DMD and accordingly the light beam is not led to the DMD. As a result, light loss is caused. This phenomenon is referred to as crosstalk in which light loss is caused by brightness interference.
The valid range of the light collection angle of each lens cell is related to the width of the lens cell. Thus, when a light beam passes through a lens cell, the valid light collection angle in the direction parallel to the short side of the lens cell is smaller than that in the direction parallel to the long side of the lens cell. In this way, when the light beam enters the lens cell at an angle greater than the valid light collection angle of the lens cells, than the travel direction of the light beam deviates from the DMD and accordingly light loss is caused. For example, in order to display a widescreen image in the 16:9 aspect ratio in a conventional projection apparatus, a DMD having an aspect ratio of 16:9 should be adopted, and in order to achieve a shaped and uniform light spot, the aspect ratio of the lens cells should also be 16:9. However, this will make the short side of each lens cell to be shorter and the valid light collection angle thereof in the direction parallel to the short side to be smaller and cause more light loss.
An illumination system capable of shaping an illumination beam is provided in Taiwan Patent No. 1300834. The illumination system includes a point light source array, a biconic lens, and a collimator lens, wherein the collimator lens is disposed between the point light source array and the biconic lens.